Seamless handoff between heterogeneous networks is a process of transferring a data session from one access network connected to a core network to another without interruption of a related service. In order to implement the seamless handoff between heterogeneous networks, IP mobility technology has been applied based on a coverage area of a wireless access zone or a policy thereof. Lately, many seamless handoff methods have been introduced. However, these seamless handoff methods do not consider properties of services that are provided over the networks.
Since the properties of services have not been considered, problems may arise during handoff. For example, a voice over Internet Protocol (VoIP) service is a real-time service and very sensitive to interruption and delay. If handoff is performed without considering the real-time property of VoIP service, the quality of the VoIP service may be seriously deteriorated due to interruption or delay occurring during the handoff.